JPS5863837A - Optical fluid analyzer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION The present invention relates to an optical analysis device for measuring the refractive index of a fluid sample.

Various techniques have been proposed for measuring the refractive index of liquids or gases. One technique uses a prism and requires measuring a critical angle. Also McGraw
-Jenkins and Wh published by Hi11 in 1957
Author: Fundamentalsof
0ptics" 6th edition, pages 257 et seq., refractive index measurement techniques based on the determination of the displacement of interference fringes are presented. Other techniques also require matching of the refractive index. requires manual and/or visual intervention by the operator to perform the process, and is therefore slow, cumbersome, and has low resolution.

The most relevant prior art is U.S. Pat. No. 3,499,712, which measures the refractive index of a liquid sample introduced into a cell (or reservoir) provided in a transparent sample holder. Discloses a device for. This cell is filled with objects (eg, spheres) of transparent material that "provide at least some liquid-solid interfaces when the liquid comes into contact with the filling material." This device measures the net amount of light transmitted (light intensity) when the cell is filled with liquid.

However, that device does not use innovative diffractive structures that are highly sensitive to changes in the refractive index and allow deviations from a predetermined refractive index value to be noted and/or corrected.

IBM 'l”echnic published June 1970
all) isclosure Bulletin, V
ow, 15. 121 discloses a diffraction refractometer using a diffraction grating immersed in the medium whose refractive index is to be measured. This device uses angles θ and θ to calculate the refractive index.
'Therefore, it is necessary to measure X and X', and the difference in intensity between diffracted light and transmitted light is not sensed and utilized.

SUMMARY OF THE INVENTION The present invention relates to a simple, efficient and non-mechanical device for rapidly measuring the refractive index of fluids (3), whether liquid or gas. This device is essentially a holographic refractometer that determines the refractive index of a fluid sample as a function of the diffraction efficiency of light diffracted by a periodic structure of known refractive index.

According to the invention, a transparent member having a known index of refraction is used which defines between a first and second portion thereof a cell for receiving a fluid sample having an unknown index of refraction. An optical fluid analysis device is provided. The first part has a diffraction grating formed on its inner surface facing the cell. The light source is positioned such that the angle of incidence with the diffraction grating satisfies the Bragg condition. The first detection means senses the intensity of the light from the light source that has been diffracted by the diffraction grating and transmitted through the sample, and the second detection means senses the intensity of the light that has passed through the diffraction grating. A device responsive to the signals generated by the first and second detection means provides an output relating to the refractive index of the sample.

(4) Description of a Preferred Embodiment The following well-known equation defines the diffraction efficiency η of a periodic sinusoidal structure.

However, as shown in FIG. 1, λ - the wavelength θ of the illumination light. - the angle of incidence d of the light with respect to the structure - the spacing between successive nodes of the sinusoidal structure, i.e. the period Δn - the refractive index between the nodes and antinodes of the structure (
(i.e. between nl and n2) - the thickness of the structure As shown in FIG. The transparent diffraction grating 10 is composed of a transparent diffraction grating 10 having a sequential spacing or period d between 0 and 13 and a grating thickness t. The member 12 and the other transparent member 13 connected thereto constitute two parts of a transparent structure with a known index of refraction n1. The elements 12 , 16 form a cell 14 partially defined by the sinusoidal surface 11 of the diffraction grating 10 . Although not shown, means are also provided for introducing into the cell 14 a liquid or gaseous substance having an unknown refractive index n2 to be determined.

Light of wavelength λ and intensity ■ is directed by a light source 15, preferably a conventional helium-neon laser or an argon laser. The light from the light source 15 has an incident angle θ such that it satisfies the Bragg condition of the following equation.

11V is incident on the surface of the diffraction grating 100.

λ==2ndsinθo(2) Diffraction efficiency η is given by the following equation.

However, ■1 is the intensity of the light diffracted by the diffraction grating 10,
Io is the intensity of light transmitted through the diffraction grating 10.

Intensity of 0th and 1st order diffracted light■. and 11, a pair of detectors 16 and 1, such as photodiodes,
7 can be provided. These detectors are equipped with a conventional discrimination circuit 18.
and circuit 18 combines the signals to provide a voltage V. The voltage ■ to Δn can be determined by the following equation.

However, 1( is a constant.

For illustration, the structure 12.13 with a change in refractive index Δn = 0.02 and a grating thickness L of 4 μ is 488 nm
Assume that it is illuminated by light of wavelength λ at an incident angle ρ1° of 20°. Under this condition, the diffraction efficiency η is 073
(7,3%).

For comparison, if we assume that the refractive index matching technique is applied to the moon, the efficiency η of light reflected from the interface with the refractive index difference 002 is as follows, which is about three orders of magnitude smaller.

(7) The apparatus according to the present invention can be used to measure the refractive index of a liquid or gas that fills the cell 14 or flows continuously through the cell. If the cell 140 dimensions are small enough that the inner wall 19 of the member 13 is virtually tangent to the sinusoidal surface 11 of the grating 10, a substance with an unknown or variable index of refraction can be introduced into the structure 12.13 by capillary action. Ru. The volume of the cell 14 may be very small as long as the grooves on the surface 11 are filled.

The analyzer described herein can also be used to indicate the condition of a fluid medium or with a servo system to adjust certain parameters to maintain a fluid at a predetermined condition. For example, the device can be used to monitor the state of charge of an electrolyte. The difference in refractive index between a fully charged electrolyte and a fully discharged electrolyte is of the order of approximately Δn = 0.02. Therefore, if transparent structures 12 and 13 having refractive indexes matched to the charged state are provided, no diffraction will occur.If force release occurs, light will be diffracted and a voltage signal representing the charged state will be obtained.

In a completely discharged state, 13% of the light becomes first-order diffracted light.

A very accurate system can be obtained by using a conventional laser 15 as the light source. However, if preferred, the laser 15 can be replaced by a light emitting diode (not shown) positioned to satisfy the Bragg condition. Detectors 16, 17 may also be replaced since the lack of coherence will only result in image blurring and not significant loss of efficiency. (if the detectors 16.
17 may be separate from member 12.13. Diffraction grating 1
0 is preferably produced by holographic recording as a surface relief in photoresist or similar material, followed by pressing or duplication into a transparent substitute of appropriate refractive index.

[Brief explanation of drawings]

FIG. 1 is a diagram showing how light from a light source is transmitted and diffracted by a diffraction grating, and FIG. 2 is a diagram of an optical fluid analysis device according to an embodiment of the present invention. 10... Diffraction grating, 11... Sinusoidal surface,
12.16...Transparent member, 14...Cell, 15
...Light source, 16.17...Detector. 1 person: Patent attorney Oka representing Internajobure Business Machines Corporation 1)
Next student (1 other person)

Claims (1)

What is claimed is: a transparent member having a known refractive index defining a region for receiving a fluid sample having an unknown refractive index and having a diffraction grating formed on an inner surface facing the region; , a light source whose incidence angle with respect to the diffraction grating is positioned so as to satisfy a diffraction condition; a first detection device for sensing the intensity of light from the light source diffracted by the diffraction grating; a second detection device for sensing the intensity of light from the light source transmitted through the grating; and an output related to the refractive index of the sample in response to signals generated by the first and second detection devices. and an optical fluid analysis device.